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Relational Quantum Mechanics

103 points by hackandthink 2y ago

hackandthink 2y ago
by Carlo Rovelli himself
AdmiralNines 2y ago
I was lost by the second sentence.
- SubiculumCode 2y ago
  Me too, but I wanted to :)
greenbit 2y ago
So .. a superposition of states would really just be a point in time during which the state variable takes no specific value? Or, it isn't so much that Schrodinger's famous cat is both alive and dead at the same time, as that it's neither? The thing about the cat in the box is that, when you later open the box, it's some kind of cat that's revealed. You don't open the box to find a nice loaf of bread. I.e., seems like something must have some kind of state, in that box, when no one is looking, that retains at least the possible outcomes and precludes others.
- uoaei 2y ago
  By some interpretations, Schrodinger's equations describe epistemological state from a given (finite) perspective. So it's not so much that the cat is both alive and dead, it's that the best we can say is that it's alive or dead. This is referred to as "quantum Bayesianism" aka QBism (pronounced "cubism"). "Observer" just refers to anything that has a direct causal connection with the thing being "observed". No consciousness necessary (grr...). If something isn't being "observed" then for all intents and purposes it exists outside of our universe and any questions about it become fundamentally irrelevant.
  - exhaze 2y ago
    Curious - how would one frame the cat before/after box reveal within the conceptual framework of causal closure?
- vehemenz 2y ago
  That something is a relation between two systems, which determines or correlates with the state of the cat/box system, but that state is not independent of the second system (observer).
markisus 2y ago
RQM is an interesting viewpoint on QM that I have not encountered before, even though it was apparently introduced in 1996. It says that the physical world is a collection of discrete events, doing away with continuous time. It also says that every event involves two systems, in that each event takes place in one system relative to another system. The idea seems a little strange but the article gives a more intuitive example. It doesn't make sense to talk about the absolute velocity of a particle, only its relative velocity with respect to a reference frame. But RQM takes it further. It brings to mind the old question about "If a tree falls in a forest and no one is around to hear it." I guess RQM would say that this question isn't even wrong. The article quickly becomes too technical for me to understand, so I'm still confused about some aspects. For instance, if each event only involves two systems, how is it that we can have a whole population of systems (eg scientists) eventually coming to a consensus about some phenomenon (eg the value of some physical quantity?) It seems necessary to have a unified global system coordinating the whole thing.
- Nevermark 2y ago
  > how is it that we can have a whole population of systems (eg scientists) eventually coming to a consensus about some phenomenon Are the scientists interacting? What is the barrier you see? I think the two systems interact simply means that any event you can measure is one you have interacted with (however indirectly). It isn't a limitation on the number of systems interacting with each other. > "If a tree falls in a forest and no one is around to hear it." I guess RQM would say that this question isn't even wrong. I think the more concrete interpretation is being used. To "hear" something, you have interacted with it in some way. Not hearing something, in any way, simply means you have not yet interacted with it. There has been no exchange of information. It doesn't mean it didn't exist. The point that there is no privileged system or observer underlines that existence isn't tied to "observers". If both we and another civilization started sending radio signals into space on the same date, and on another future date both civilizations finally got the first signals from the other, neither detection caused the other civilization to come into existence. They both existed separately before the common detection. There is no privileged observer from whom to relate what exists or not by their observations. Yes, trees that fall in a forest without human beings cause vibrations. They interact with the forest around them. There is no observer-tron particle in humans that acts in a special way on events around us. But between a photon being emitted and absorbed (two bracketing events on its existence), we might say the photon's path is just those interactions, and there isn't anything to talk about between them. If it had no interactions with anything else between its two bracketing events. Like a discrete edge in a simple graph, it is a connection between two nodes, there are no dynamics in between the nodes. An edge is just a connection, not a continuous path.
anon291 2y ago
This is interesting to me. Some of the various paradoxes are resolved, but now consciousness does become even more important, because I cannot escape from the fact that my perspective (which is unique to me according to RQM) still seems very real. Now the entirety of the universe is literally an observation that I (and I alone) experience. But then why do I 'feel' like it happened. Do other things feel like things happened to them? Am I the only one out here?
- meneton 2y ago
  No I'm here too. But we are not totally correlated. There is more correlation within you, than there is between you and me. We are both nodes in the universe's correlation network complex enough to model our own correlations.
lisper 2y ago
Gotta put in a plug for QIT, which is very similar, but I think a little easier to understand: https://arxiv.org/abs/quant-ph/9512022 https://arxiv.org/abs/quant-ph/9512022 and a more accessible version that I wrote a long time ago: https://flownet.com/ron/QM.pdf https://flownet.com/ron/QM.pdf
katabasis 2y ago
I'm a fan of Carlo Rovelli's popular science books. "The Order of Time" in particular left a big impression on me. He is a philosopher as well as a scientist, and he has a gift for writing beautiful and accessible prose about some pretty heady topics. If you are interested in RQM but find this article somewhat dry, check out his short book "Helgoland". I find both RQM and Rovelli's notion of "thermal time" (i.e. the idea causality and entropy are emergent properties dependent on our perspective, as opposed to fundamental features of reality) to be very convincing.
- babycheetahbite 2y ago
  I just finished Rovelli's "Reality Is Not What It Seems" last weekend and enjoyed it. It is a broad and high level summary of the progress of physics and the book ends with some of the more speculative ideas being pursued. I especially enjoyed the "thermal time" ideas you mention, which he touches on in this book.
moi2388 2y ago
“ double (a) variables only take value at discrete interactions and (b) the value a variable takes is only relative to the (other) system affected by the interaction.” Layperson here. Can I read this as saying yes to locality, no to realism, and violation of causality since this only depends on who measured it, another interaction could interpret cause and effect differently?

103 points by hackandthink 2y ago

hackandthink 2y ago

by Carlo Rovelli himself

AdmiralNines 2y ago

I was lost by the second sentence.

SubiculumCode 2y ago
Me too, but I wanted to :)

greenbit 2y ago

So .. a superposition of states would really just be a point in time during which the state variable takes no specific value? Or, it isn't so much that Schrodinger's famous cat is both alive and dead at the same time, as that it's neither? The thing about the cat in the box is that, when you later open the box, it's some kind of cat that's revealed. You don't open the box to find a nice loaf of bread. I.e., seems like something must have some kind of state, in that box, when no one is looking, that retains at least the possible outcomes and precludes others.

uoaei 2y ago
By some interpretations, Schrodinger's equations describe epistemological state from a given (finite) perspective. So it's not so much that the cat is both alive and dead, it's that the best we can say is that it's alive or dead. This is referred to as "quantum Bayesianism" aka QBism (pronounced "cubism"). "Observer" just refers to anything that has a direct causal connection with the thing being "observed". No consciousness necessary (grr...). If something isn't being "observed" then for all intents and purposes it exists outside of our universe and any questions about it become fundamentally irrelevant.
- exhaze 2y ago
  Curious - how would one frame the cat before/after box reveal within the conceptual framework of causal closure?
vehemenz 2y ago
That something is a relation between two systems, which determines or correlates with the state of the cat/box system, but that state is not independent of the second system (observer).

markisus 2y ago

RQM is an interesting viewpoint on QM that I have not encountered before, even though it was apparently introduced in 1996. It says that the physical world is a collection of discrete events, doing away with continuous time. It also says that every event involves two systems, in that each event takes place in one system relative to another system. The idea seems a little strange but the article gives a more intuitive example. It doesn't make sense to talk about the absolute velocity of a particle, only its relative velocity with respect to a reference frame. But RQM takes it further. It brings to mind the old question about "If a tree falls in a forest and no one is around to hear it." I guess RQM would say that this question isn't even wrong. The article quickly becomes too technical for me to understand, so I'm still confused about some aspects. For instance, if each event only involves two systems, how is it that we can have a whole population of systems (eg scientists) eventually coming to a consensus about some phenomenon (eg the value of some physical quantity?) It seems necessary to have a unified global system coordinating the whole thing.

Nevermark 2y ago
> how is it that we can have a whole population of systems (eg scientists) eventually coming to a consensus about some phenomenon Are the scientists interacting? What is the barrier you see? I think the two systems interact simply means that any event you can measure is one you have interacted with (however indirectly). It isn't a limitation on the number of systems interacting with each other. > "If a tree falls in a forest and no one is around to hear it." I guess RQM would say that this question isn't even wrong. I think the more concrete interpretation is being used. To "hear" something, you have interacted with it in some way. Not hearing something, in any way, simply means you have not yet interacted with it. There has been no exchange of information. It doesn't mean it didn't exist. The point that there is no privileged system or observer underlines that existence isn't tied to "observers". If both we and another civilization started sending radio signals into space on the same date, and on another future date both civilizations finally got the first signals from the other, neither detection caused the other civilization to come into existence. They both existed separately before the common detection. There is no privileged observer from whom to relate what exists or not by their observations. Yes, trees that fall in a forest without human beings cause vibrations. They interact with the forest around them. There is no observer-tron particle in humans that acts in a special way on events around us. But between a photon being emitted and absorbed (two bracketing events on its existence), we might say the photon's path is just those interactions, and there isn't anything to talk about between them. If it had no interactions with anything else between its two bracketing events. Like a discrete edge in a simple graph, it is a connection between two nodes, there are no dynamics in between the nodes. An edge is just a connection, not a continuous path.

anon291 2y ago

This is interesting to me. Some of the various paradoxes are resolved, but now consciousness does become even more important, because I cannot escape from the fact that my perspective (which is unique to me according to RQM) still seems very real. Now the entirety of the universe is literally an observation that I (and I alone) experience. But then why do I 'feel' like it happened. Do other things feel like things happened to them? Am I the only one out here?

meneton 2y ago
No I'm here too. But we are not totally correlated. There is more correlation within you, than there is between you and me. We are both nodes in the universe's correlation network complex enough to model our own correlations.

lisper 2y ago

Gotta put in a plug for QIT, which is very similar, but I think a little easier to understand: https://arxiv.org/abs/quant-ph/9512022 https://arxiv.org/abs/quant-ph/9512022 and a more accessible version that I wrote a long time ago: https://flownet.com/ron/QM.pdf https://flownet.com/ron/QM.pdf

katabasis 2y ago

I'm a fan of Carlo Rovelli's popular science books. "The Order of Time" in particular left a big impression on me. He is a philosopher as well as a scientist, and he has a gift for writing beautiful and accessible prose about some pretty heady topics. If you are interested in RQM but find this article somewhat dry, check out his short book "Helgoland". I find both RQM and Rovelli's notion of "thermal time" (i.e. the idea causality and entropy are emergent properties dependent on our perspective, as opposed to fundamental features of reality) to be very convincing.

babycheetahbite 2y ago
I just finished Rovelli's "Reality Is Not What It Seems" last weekend and enjoyed it. It is a broad and high level summary of the progress of physics and the book ends with some of the more speculative ideas being pursued. I especially enjoyed the "thermal time" ideas you mention, which he touches on in this book.

moi2388 2y ago

“ double (a) variables only take value at discrete interactions and (b) the value a variable takes is only relative to the (other) system affected by the interaction.” Layperson here. Can I read this as saying yes to locality, no to realism, and violation of causality since this only depends on who measured it, another interaction could interpret cause and effect differently?